Heater with Internal Temperature Sensors

ABSTRACT

A heater for heating air includes an inlet, an outlet, and an air duct between the inlet and the outlet. A fan and a heating element are positioned in the air duct. A first temperature sensor is positioned at or near the inlet and configured to measure a first temperature of ambient air at the inlet. A second temperature sensor in positioned in the air duct and configured to measure a second temperature of heated air flowing through the air duct. The heater is configured to control heating power and fan speed based on measurements taken by the first and second temperature sensors.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 63/283,982 filed Nov. 29, 2021, titled “HEATER WITH INTERNAL TEMPERATURE SENSORS,” the content of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The invention relates to a heater and in particular, a heater having internal temperature sensors for regulating the air temperature within the heater and controlling certain operations of the heater.

BACKGROUND

A known type of heater such as a space heater is configured to intake air from the ambient space around the heater (e.g., an interior room of a building), heat the intaken air, and then discharge the heated air back into the ambient space to heat the ambient space to a desired temperature. In a typical heater of known design, a temperature sensor is located near the air inlet of the heater to measure the temperature of the ambient air. The temperature sensor is then used to control the operation of the heater by comparing the ambient temperature to a target temperature set by the user for the heater to heat the ambient space. If the difference between the ambient temperature and the target temperature is greater than a predetermined threshold value, the heater may continue to operate at its current settings. On the other hand, if the difference between the ambient temperature and the target temperature is less than a predetermined threshold value, the heater (or at least its heating element(s)) may shut down.

Typically, the temperature sensor used in such application is a thermistor, particularly a negative temperature coefficient (NTC) sensor. Other temperature sensors that may be used include The NTC sensor is then used to control the operation of the heater by comparing the ambient temperature to target or set values for the heater to heat the air around the heater (i.e., the ambient air). In some applications, a resistance temperature detector (RTD), thermocouple, or other type of heating probe or thermometer can used in place of an NTC sensor.

In known heaters, temperature sensors configured as just described can be effective in regulating the temperature of the air outputted by the heater. However, as currently implemented in known heaters, temperature sensors are not designed to control the heater in response to conditions that may impair the operation of the heater. As examples, the temperature sensors are not designed to (i) react to blockages on the inlet or outlet of the heater that can cause the heater itself to overheat; (ii) react to heater malfunctions; or (iii) safely respond to a slow start of a fan motor of the heater.

There is an ongoing need for further developments in heaters of the type just described.

SUMMARY

To address the foregoing problems, in whole or in part, and/or other problems that may have been observed by persons skilled in the art, the present disclosure provides methods, processes, systems, apparatus, instruments, and/or devices, as described by way of example in implementations set forth below.

According to an implementation the present disclosure, a heater for heating air includes: a housing comprising an inlet, an outlet, and an air duct between the inlet and the outlet; a fan positioned in the air duct and configured to establish a flow of air from an ambient space outside the housing into the inlet, through the air duct, and to the outlet; a heating element positioned in the air duct and configured to heat the air flowing through the air duct; a first temperature sensor positioned at or near the inlet and configured to measure a first temperature of ambient air at the inlet; and a second temperature sensor positioned in the air duct and configured to measure a second temperature of heated air flowing through the air duct.

In an implementation, the heater includes a controller configured to control a preset heating power of the heating element and a preset fan speed of the fan according to any of the methods disclosed herein.

According to an implementation the present disclosure, a method for operating a heater includes: operating the heater at a preset heating power of a heating element of the heater and a preset fan speed of a fan of the heater, to intake ambient air through an inlet of the heater and into an air duct of the heater, heat air in the air duct, and discharge the heated air through an outlet of the heater; making a first measurement of a first temperature of the ambient air at the inlet; making a second measurement of a second temperature of heated air in the air duct; and determining if one or more criteria have been met, wherein the one or more criteria are based on the second measurement, or both the first measurement and the second measurement, and wherein: if none of the one or more criteria has been met, continuing to operate the heater at the preset heating power and the preset fan speed; and if any of the one or more criteria has been met, adjusting the preset heating power, or adjusting the preset fan speed, or adjusting both the preset heating power and the preset fan speed.

Other devices, apparatus, systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views.

FIG. 1 is a cross-sectional, longitudinal side view of an example of a heater according to an implementation of the present disclosure.

FIG. 2 is a schematic view of an example of a controller for a heater according to an implementation of the present disclosure.

FIG. 3 is a flow diagram illustrating an example of a method for operating a heater according to an implementation of the present disclosure.

The illustrations in the drawing figures are considered to be schematic, unless specifically indicated otherwise.

DETAILED DESCRIPTION

In this disclosure, all “aspects,” “examples,” “embodiments,” and “implementations” described are considered to be non-limiting and non-exclusive. Accordingly, the fact that a specific “aspect,” “example,” “embodiment,” or “implementation” is explicitly described herein does not exclude other “aspects,” “examples,” “embodiments,” and “implementations” from the scope of the present disclosure even if not explicitly described. In this disclosure, the terms “aspect,” “example,” “embodiment,” and “implementation” are used interchangeably, i.e., are considered to have interchangeable meanings.

In this disclosure, the term “substantially,” “approximately,” or “about,” when modifying a specified numerical value, may be taken to encompass a range of values that include +/−10% of such numerical value.

FIG. 1 is a cross-sectional, longitudinal side view of an example of a heater (or heating device) 100 according to an implementation of the present disclosure. The heater 100 may be utilized to heat the ambient space outside the heater 100. The ambient space may be, for example, a room inside a building, an interior of a vehicle, etc. The heater 100 is configured to intake (draw in) ambient air, heat the intaken air, and discharge the heated air into the ambient space. The heater 100 may be a standalone device or be part of another device that performs functions other than heating. The heater 100 may be a product such as a consumer (commercially available) product. As one example, the heater 100 may be a space heater.

The heater 100 includes a housing or enclosure 104 that may be defined by one or more structural members. The housing 104 may have a rectilinear shape as shown, or may have any other polygonal shape or alternatively a rounded shape (e.g., spherical, ovoid, cylindrical, etc.). At least for purposes of description and illustration, the heater 100 (or housing 104) may be considered as being arranged around and along a device axis L, which may be (at least in a general sense) the central axis of the heater 100 (or housing 104). The heater 100 (or at least the housing 104) generally has an inlet side 108, an outlet side 112, a top side 116 between the inlet side 108 and the outlet side 112, a bottom side 120 between the inlet side 108 and the outlet side 112, and lateral sides 124 (of which only one lateral side 124 is viewable in FIG. 1 ) between the inlet side 108 and the outlet side 112. Relative to the device axis L and from the perspective of the side view of FIG. 1 , the inlet side 108 and outlet side 112 are axially opposite to each other, and the top side 116 and bottom side 120 are radially opposite to each other. Depending on the shape of the housing 104, the top side 116, bottom side 120, and lateral sides 124 may or may not be adjoined at distinct corners.

The housing 104 encloses or surrounds a device interior that includes an air inlet 128 at the inlet side 108, an air outlet 132 at the outlet side 112, and an air duct 136 arranged along the device axis L between the air inlet 128 and the air outlet 132. By this configuration, the housing 104 defines an air flow path running through the heater 100 from the air inlet 128, through the air duct 136, and to the air outlet 132. In the example of FIG. 1 , the air duct 136 and device axis L are straight. Alternatively, all or part of the air duct 136 and device axis L may be curved. In this disclosure, the term “axial” or “axially” relates to the device axis L and is not limited to a straight line (e.g., is not necessarily correspond to an axis of a Cartesian coordinate system).

The housing 104 also includes a fan 140 and one or more heating elements 144 positioned in the air duct 136 by any appropriate mounting means. Generally, the fan 140 may have any configuration appropriate for use in a heater of the type described herein. Generally, the fan 140 has a configuration effective to establish an air flow (flow of air) 148 (depicted by a large arrow in FIG. 1 ) running from the ambient space into the air inlet 128, through the air duct 136, and to the air outlet 132. In the illustrated example, the fan 140 includes fan blades 152 attached to a fan hub 156, which in turn is attached to a motor shaft 160. The motor shaft 160 is coupled to a fan motor 164. In operation, the fan motor 164 drives rotation of the motor shaft 160 and thus also the fan hub 156 and the fan blades 152. The motor 164 is typically an electric motor of a type appropriate for use in a heater of the type described herein, taking into account factors such as the size of the air duct 136, the intended ranges of fan speed and air flow rate, etc. The motor 164 is typically capable of varying the fan speed of the fan 140.

Generally, the heating element 144 may have any configuration appropriate for use in a heater of the type described herein. As one example, the heating element 144 may generate heat according to a heating mechanism based on electrical resistance (i.e., Joule, or ohmic, heating). In other words, the heating element 144 may generate and emit heat energy in response to application of a voltage to the heating element 144, which generates an electrical current through the heating element 144. Thus, for example, the heating element 144 may be or include one or more electrically conductive wires or coils. The amount of heat generated by the heating element 144 depends on the level (or amount, magnitude, etc.) of heating power (or wattage) at which the heating element 144 is operating. Typically, the heating element 144 is configured such that the (level of) heating power is variable, thereby allowing selective variation in (or adjustment to) the temperature to which the air is heated in the air duct 136.

In one implementation, the heating element 144 represents two or more distinct heating elements, each operable at two or more settings of heating power. Different combinations of the heating elements may be active, with each heating element being individually set to a certain heating power. By this configuration, the heating element 144 is operable at a finite number of levels of heating power. The different combinations may be referred to as stages of the heating element operation. An example of such a heating element 144 is shown in the Table 1 below.

TABLE 1 Heating Element Logic Triac A Triac B Triac C Triac D Heat element Stage 1 1 0 1 0 1500 Stage 2 1 0 0 1 1200 Stage 3 0 1 1 0 1050 Stage 4 0 1 0 1 750 Stage 5 0 0 1 0 600 Stage 6 0 1 0 0 450 Stage 7 0 0 0 0 OFF 900 W Heat Ring 600 W Heat Ring (Watts)

Generally, the fan 140 and the heating element 144 may be positioned anywhere in the air duct 136. In the illustrated example, the fan 140 is positioned nearer to the air inlet 128 than the heating element 144, and the heating element 144 is positioned nearer to the air outlet 132 than the fan 140. Accordingly, relative to the device axis L, the fan 140 is positioned between the heating element 144 and the air inlet 128, and the heating element 144 is positioned between the fan 140 and the air outlet 132. By this configuration, the fan 140 may be located in the upstream region of the air duct 136 that is cooler than the downstream region where the heating element 144 is located (depending on whether a temperature difference exists between the ambient air entering the air inlet 128 and the air heated by the heating element 144. The fan 140 may be spaced from the heating element 144 at a distance sufficient to prevent the fan motor 164 from being overheated by the heating element 144.

The flow (or flow path) of air 148 through the air duct 136 (as driven by the fan 140) may be considered as including at least three portions: unheated ambient air 168 at and near the air inlet 128, which is drawn into and through the air inlet 128 and driven towards the fan 140 and the heating element 144; internal (heated) air 172 in the air duct 136 in the vicinity of the heating element 144, which is being (or has been) heated by the heating element 144; and discharged or outputted (and heated) air 176 that is discharged from the air duct 136 through the air outlet 132 after being heated by the heating element 144.

The heater 100 also includes a first (or primary) temperature sensor 180 and a second (or secondary) temperature sensor 184. The first temperature sensor 180 may be positioned at or near the air inlet 128 by any appropriate mounting means, and is configured to measure a first temperature of the ambient air 168 at the air inlet 128. In the present context, “near” means that the first temperature sensor 180 is positioned close enough to the air inlet 128 to ensure accurate temperature readings of the ambient air 168, particularly before the ambient air 168 starts to become heated by the downstream heating element 144. In the illustrated example, the first temperature sensor 180 is positioned upstream of the fan 140. The first temperature sensor 180 may be positioned either inside or outside the air duct 136.

The second temperature sensor 184 is positioned in the air duct 136 by any appropriate mounting means, and is configured to measure a second temperature of the internal air 172 flowing through the air duct 136. More specifically, the second temperature is the temperature of the internal air 172 after it has been heated by the heating element 144 and has not yet had an opportunity to lose an appreciable amount of the heat energy deposited by the heating element 144. For this purpose, in an implementation, the second temperature sensor 184 is located at or near the heating element 144. In the present context, “at” means that the second temperature sensor 184 is positioned at the same (or substantially the same) axial position as the heating element 144 but is radially spaced from the heating element 144 (e.g., over or under the heating element 144). Also in the present context, “near” means that the second temperature sensor 184 is positioned between the second temperature sensor 184 and the air outlet 132. In this latter case, it may be advantageous to locate the second temperature sensor 184 closer to the heating element 144 than to the air outlet 132 to ensure temperature measurements are taken before the internal, heated air 172 starts to cool down as it flows away from the heating element 144. In the illustrated example, the first temperature sensor 180 is positioned at the top side of the air duct 136, and the second temperature sensor 184 is positioned at the bottom side of the air duct 136.

The functions of the first temperature sensor 180 and the second temperature sensor 184 are described further below. Examples of a device that may be utilized as the first temperature sensor 180 and the second temperature sensor 184 include, but are not limited to, a thermistor (particularly a negative temperature coefficient (NTC) sensor), a resistance temperature detector (RTD), and a thermocouple. In an implementation, the first temperature sensor 180 and the second temperature sensor 184 are identical. For example, both may be 100 kΩ NTC sensors.

The heater 100 also includes one or more user input devices and user output devices, which in the illustrated example are combined as a single user interface 188. The user interface 188 is typically mounted to an outside surface of the heater 100 (e.g., the housing 104) to facilitate access by the user and to thermally isolate the user interface 188 from the heating element 144. Examples of user input devices include a user-pressable button, key, or the like for switching the heater 100 between on and off states, and buttons that allow the user to set or select a desired (target) temperature at which the heater 100 is to output air. Other examples may include, but are not limited to, buttons that allow the user to set or select a desired fan speed, mode of operation (e.g., LOW heat, HIGH heat, FAN ONLY, etc.), a timer that sets the duration of operation of the heater 100 before automatically powering down, controls for a display screen (e.g., for setting the brightness of the display screen, customizing the information displayed, etc.), etc. The display screen typically displays the current ambient temperature (as measured by the first temperature sensor 180), the target temperature set by the user, and various other information relating to the operation of the heater 100. Examples of user output devices include the display screen (typically a liquid crystal display (LCD) screen) and often backlighting for one or more of the user input buttons. Other examples may include, but are not limited to, light emitting diodes (LEDs) utilized as indicators of operational states of the heater 100 or other information, and one or more speakers to provide auditory outputs.

The heater 100 also includes a system controller (or controller controller, or computing device) 192 in signal (electrical) communication (either wired or wirelessly) with the heating element 144, the fan 140 (e.g., fan motor 164 or associated electrical circuitry), and the user interface 188. The controller 192 may be positioned outside or inside the heater 100, in either case at a location where the controller 192 will not be overheated by the heating device 144. The controller 192 is configured to control the heating power and the fan speed, and receive and process measurement signals outputted by the first temperature sensor 180 and the second temperature sensor 184, as described below by way of example. The controller 192 is also configured to control the functions of the user interface 188, including receiving and processing user inputs to the user interface 188 and presenting information at the display screen. For all such purposes, the controller 192 may include any suitable combination of hardware, firmware, software, etc., including one or more electronics-based processors and memories, as appreciated by persons skilled in the art. For example, the controller 192 may include a non-transitory (or tangible) computer-readable medium that includes non-transitory instructions for performing any of the methods disclosed herein. A further example of the controller 192 is described below in conjunction with FIG. 2 .

As a general example of a method for operating the heater 100, the fan 140 is operated to establish the flow of air 148 through the heater 100 and the heating element 144 is operated to heat the air 148 as the air 148 flows through the heater 100. Specifically, the ambient air 168 is intaken through the air inlet 128 and into the air duct 136, the internal air 172 in the air duct 136 is heated via heat transfer from the heating element 144, and the heated air 176 is discharged from the air duct 136 through the air outlet 132. In this method, the heating element 144 is operated at a preset (or predetermined, setpoint, desired, selected, target, etc.) heating power, and the fan 140 is operated at a preset (or predetermined, setpoint, desired, selected, target, etc.) fan speed. The heater 100 is configured to allow the user to set or select the target temperature (e.g., 70° F.) at which the heater 100 is to heat the ambient space—i.e., the temperature of the discharged air 176. The target temperature is dictated by the level of heating power applied to the heating element 144 or at which the heating element 144 operates. Thus, setting the target temperature in effect corresponds to setting the heating power. In some implementations, the heater 100 may also allow the user to set or select a target fan speed (e.g., a low speed or high speed, or a variable range of fan speed).

In an implementation, the controller 192 determines the level of heating power, or both heating power and fan speed, based on a comparison of the ambient temperature measured by the first temperature sensor 180 and the target temperature inputted by the user at the user interface 188. For example, the controller 192 may calculate the temperature difference, ΔT, between the measured ambient temperature (ROOM TEMP) and the user-requested target temperature (SET TEMP) as follows.

ΔT=ROOM TEMP−SET TEMP

In an implementation, the value for the ambient temperature utilized to calculate the temperature difference may be a running average of several temperature readings, as described in detail below.

In an implementation, if the controller 192 determines that the temperature difference is greater than a predetermined first threshold value, the controller 192 may increase the heating power at which the heating element 144 operates, which may also involve switching on the heating element 144 if currently off, and/or adjusting the fan speed. On the other hand, if the controller 192 determines that the temperature difference is less than a predetermined second threshold value (which may be different from the first threshold value), the controller 192 may allow the heater 100 (in particularly, the heating element 144 and fan 140) to continue operating at its current settings. The process of interrogating the first temperature sensor 180, making determinations, and possibly making adjustments may be done at a predetermined loop rate (i.e., frequency, or intervals of time between executing the process).

In an implementation, in addition to the temperature difference ΔT, the fan 140 and the heating element 144 are controlled by different modes of operation, which may be set by the user or in some situations set by the controller 192. Examples of modes of operation include the above-noted LOW heat, HIGH heat, and FAN ONLY modes. Other modes may be provided, for example a MEDIUM heat mode. Table 2 below shows an example of a LOW heat mode, and Table 3 below shows an example of a HIGH heat mode.

TABLE 2 Heating Element and Fan Speed Function in LOW mode Heat element Fan Speed ΔT (° F.) (W) (RPM) Stage 1  −∞ < ΔT ≤ −0.3 750 1511 Stage 2 −0.3 < ΔT ≤ 0    750 1511 Stage 3   0 < ΔT ≤ 0.3 750 1511 Stage 4 0.3 < ΔT ≤ 0.6 750 1511 Stage 5 0.6 < ΔT ≤ 0.9 600 1350 Stage 6 0.9 < ΔT ≤ 4  450 1205 Stage 7  4 < ΔT ≤ +∞ OFF OFF

TABLE 3 Heating Element and Fan Speed Function in HIGH mode Heat element Fan Speed ΔT (° F.) (W) (RPM) Stage 1  −∞ < ΔT ≤ −0.3 1500 2250 Stage 2 −0.3 < ΔT ≤ 0    1200 1961 Stage 3  0 < ΔT ≤ 0.3 1050 1800 Stage 4 0.3 < ΔT ≤ 0.6 750 1511 Stage 5 0.6 < ΔT ≤ 0.9 600 1350 Stage 6 0.9 < ΔT ≤ 4  450 1205 Stage 7  4 < ΔT ≤ +∞ OFF OFF

In the FAN ONLY mode, the heating element is OFF and the fan speed is set to a predetermined level such as, for example, the maximum fan speed, which in this example is 2250 RPM.

In an implementation, the controller 192 may utilize values for the measured ambient temperature (ROOM TEMP) and the user-requested target temperature (SET TEMP) to determine if a user-inputted mode of operation should be overridden and the heater 100 switched to a different mode (or the heating element 144 and/or fan 140 adjusted to a different setting) or even powered down entirely.

As one example, the controller 192 may determine if the following condition (or criterion) is being met: ROOM TEMP>SET TEMP+1° F. If so, the controller 192 may switch the mode of operation from HIGH heat to LOW heat, unless the heater 100 is already operating in the LOW heat mode. Then, the controller 192 may maintain the LOW heat mode until ROOM TEMP=SET TEMP, at which time the controller 192 restore the ability to receive user input. On the other hand, if the heater 100 is already operating in the LOW heat mode, the controller 192 may power down the heater 100. Other constant values may be substituted for 1° F., as needed for effective control.

As another example, if the controller 192 determines that ROOM TEMP>SET TEMP+4° F., the controller 192 may power down the heater 100. Other constant values may be substituted for 4° F., as needed for effective control.

As another example, if the controller 192 determines that ROOM TEMP is ever greater than a predetermined high threshold value (e.g., 120° F.) or less than a predetermined low threshold value (e.g., 0° F.), the controller 192 may power down the heater 100. In this situation, it is assumed that the first temperature sensor 180 or associated circuitry has failed.

According to a further aspect of the present disclosure, the controller 192 controls operations of the heater 100 based also on reading temperature measurements (measurement signals) produced by the second temperature sensor 184 (values of 2^(nd) TEMP), and/or reading temperature measurements (measurement signals) produced by both the first temperature sensor 180 (values of ROOM TEMP) and the second temperature sensor 184, including calculating (or detecting) and analyzing (or assessing) the temperature difference between a first temperature measurement received from (i.e., a first value of temperature measured by) the first temperature sensor 180 and a second temperature measurement received from (i.e., a second value of temperature measured by) the second temperature sensor 184. In one or more implementations of the heater 100 as described herein, it has been found that when the heater 100 is operating normally and under steady-state operating conditions, the detected temperature difference between the readings of the first temperature sensor 180 and the second temperature sensor 184 is generally demonstrated to be less than 5° C. and typically less than 3° C. Moreover, heat transfer occurs almost entirely between the heating element 144 and the air passing through the air duct 136. Little to none of the heat is wasted by raising the temperature of the housing 104 of the heater 100. According to a further aspect of the present disclosure, the controller 192 utilizes the temperature difference between the readings of the first temperature sensor 180 and the second temperature sensor 184, as well as readings acquired from the first temperature sensor 180 and the second temperature sensor 184 individually, to determine if the heater 100 is operating normally or abnormally (e.g., outside of normal ranges) and determine what actions need to be taken if the detected temperature difference (and/or individual first and/or second temperature measurements) are outside of the normal ranges. In this way, the second temperature sensor 184 may serve as an additional protective device for the heater 100.

In an implementation, the controller 192 may override operational modes such as shown in Tables 2 and 3 above based (at least in part) on readings taken by the second temperature sensor 182. As an example, if the controller 192 determines that 2^(nd) TEMP≤ROOM TEMP+20° F., the controller 192 may switch or adjust the operations of the heating element 144 and the fan 140 according to the following Table 4. Other constant values may be substituted for 20° F., as needed for effective control.

TABLE 4 Secondary Temperature Sensor Function Elapsed Time Heat element Fan operation 0 seconds Increase (1) heater stage Motor speed remains at number/reduce wattage stage/No RPM change 2 seconds Increase additional (2) heater Decrease one stage/Increase stage numbers/reduce wattage RPM to the previous stage 4 seconds Increase additional (2) heater Decrease one stage/Increase stage numbers/reduce wattage RPM to the previous stage 6 seconds Turn heater element off Change to Stage 1/Increase RPM to maximum

Continuing with this example, when the controller 192 detects that 2^(nd) TEMP<ROOM TEMP+20° F. for 10 seconds, the controller 192 returns the heater 100 to normal operations. On the other hand, if the controller 192 determines the 2^(nd) TEMP has not returned to less than ROOM TEMP+20° F. within 30 seconds, then the controller 192 may power down the heater 100. Other constant values may be substituted for 20° F., and other time durations may be substituted for 10 or 30 seconds, as needed for effective control.

In an implementation, if the controller 192 determines that 2^(nd) TEMP is ever greater than a predetermined high threshold value (e.g., 120° F.) or less than a predetermined low threshold value (e.g., 0° F.), the controller 192 may power down the heater 100. In this situation, it is assumed that the second temperature sensor 184 or associated circuitry has failed.

In an implementation, the second temperature sensor 184 functions as a way to remove heat from the heater 100 during the operation of powering down the heater 100. For example, when the heater 100 is powering down (by input from the user or action taken by the controller 192), the heating element 192 may be deenergized immediately (turned OFF) while the fan 140 continues to operate, for example at the above-noted Stage 4, until a condition (or criterion) is met. For example, the fan 140 may continue to run until 2^(nd) TEMP<ROOM TEMP+10° F., or until 30 seconds have passed, whichever occurs first, at which time the fan turns OFF. Other constant values may be substituted for 1° F., and other time durations may be substituted for 30 seconds, as needed for effective control.

In an implementation, the first temperature measurement and the second temperature measurement are both taken (typically simultaneously) at a predetermined loop rate. For example, the loop rate may be set to 5 Hertz (Hz), in which case the first and second temperature measurements are taken every 200 milliseconds (ms). Lower loop rates may be utilized. However, if the loop rate is too low, the system may not be able to react rapidly enough to achieve effective control over the operations of the heater 100. As one example, loop rates higher than 2 Hz may be recommended.

In an implementation, a running average of a predetermined number of simultaneous readings of each of the first temperature measurement and the second temperature measurement are taken. For example, an average of ten simultaneous readings may be concurrently taken before applying the running average. The averaging equation for the first temperature measurement (taken by the first temperature sensor 180), T_(Room), and the second temperature measurement (taken by the second temperature sensor 184), T_(2NTC), is shown below.

${T_{Room} = \frac{\Sigma_{i = 1}^{i = {10}}T_{i}}{10}};{T_{2NTC} = \frac{\Sigma_{i = 1}^{i = {10}}T_{i}}{10}}$

For example, at time t=0 seconds, ten concurrent readings of temperature (e.g., T_(Room)) are made:

1. T₁=74.5° F.

2. T₂=79.3° F.

3. T₃=74.8° F.

4. T₄=73.6° F.

5. T₅=70.9° F.

6. T₆=74.1° F.

7. T₇=74.2° F.

8. T₈=74.7° F.

9. T₉=73.9° F.

10. T₁₀=74.4° F.

These temperatures are averaged according to the equation above to provide the temperature average, T_(average):

$T_{average} = \frac{\Sigma_{i = 1}^{i = {10}}T_{i}}{10}$ $T_{average} = \frac{T_{1} + T_{2} + T_{3} + T_{4} + T_{5} + T_{6} + T_{7} + T_{8} + T_{9} + T_{10}}{10}$ $T_{average} = {\frac{{7{4.5}} + {7{9.3}} + {7{4.8}} + {7{3.6}} + {7{0.9}} + {7{4.1}} + {7{4.2}} + {7{4.7}} + 73.9 + {7{4.4}}}{10} = {7{4.4}4}}$

The calculation above represents the first calculated value, so the initial value of the running average, T_(running_average), will be 74.44, from the definition above. In other words, the initial value the running average is T_(running_average)=T_(average).

The ten simultaneous readings may be repeated at a predetermined frequency, for example every 30 seconds. Assume for example, that over the next 150 seconds the T_(average) values are: 74.44, 74.94, 73.81, 74.58, 78.10, and 74.73. Then, the T_(running_average) values are calculated according to the equation below, where t is the current time, (t×1) is the time of the previous calculation, and α is a weighting factor that in this example is set to be 0.84.

T _(running_average)(t)=ROOM TEMP=α*T _(average)+(1−α)*T _(running_average)(t−1)

T _(running_average)0=(0.84*74.44)+(0.16*74.44)=74.44→User Interface=74

T _(running_average)1=(0.84*74.94)+(0.16*74.44)=74.52→User Interface=74

T _(running_average)2=(0.84*73.81)+(0.16*74.52)=74.41→User Interface=74

T _(running_average)3=(0.84*74.58)+(0.16*74.41)=74.43→User Interface=74

T _(running_average)4=(0.84*78.10)+(0.16*74.43)=75.02→User Interface=75

T _(running_average)5=(0.84*74.73)+(0.16*75.02)=74.97→User Interface=74

In the above calculations for running average, in the case of room (ambient) temperature values, the terms to the right of the arrow (e.g., User Interface=74) represent an optional operation in which the calculated running average is rounded down and then displayed by the user interface 188 as the current indication of ambient temperature. Thus, in the above example, the running average at time t=0 is calculated to be 74.44, so the displayed temperature value is rounded down to 74.

Once the running average of simultaneous readings of each of the first temperature sensor 180 the second temperature sensor 184 is determined, the temperature difference between the first measured temperature and the second measured temperature is then calculated using the following equation:

ΔT=T _(2NTC) −T _(Room)

Once more than one successive temperature difference is calculated over time, the rate of temperature change can be calculated by dividing the difference between two successive temperature differences by the time that has passed between the measurements, according to the following equation.

$\overset{˙}{T} = \frac{{\Delta T_{i}} - {\Delta T_{i - 1}}}{\Delta t}$

From the first and second temperature measurements made (or running averages calculated from the first and second temperature measurements), and/or additionally from the calculations based on the first and second temperature measurements such as the temperature difference between the first and second temperature measurements and/or the measured rate of change, it can be determined how to control the heater 100. In an implementation, the controller 192 is configured to receive the first and second temperature measurements (i.e., measurement signals from the first temperature sensor 180 and the second temperature sensor 184 that are indicative of values corresponding to the first and second temperature measurements) and, based on these measurements, determine whether any aspect of the current operation of the heater 100 (in particular, heating power, fan speed, and on/off state of the heather 100) should be adjusted.

In an implementation, the controller 192 utilizes the temperature measurements and related calculations to determine if one or more criteria (control criteria, or operational criteria) have been met (or are “true”). If none of the criteria have been met (or all are “false”), then the controller 192 takes no remedial action and allows the heater 100 to continue to operate at its current settings. In other words, if none of the criteria have been met, the heater 100 is considered to be operating normally. The criteria may be formulated to enable the controller 192 to respond to various conditions that may cause the heater to overheat or malfunction. Such conditions may include a blockage on the air inlet 128 or the air outlet 136 that impairs proper air flow, malfunctioning of the fan 140, malfunctioning of the heating element, and malfunctioning of circuitry associated with any of the components of the heater 100. Six examples of criteria are as follows.

A first criterion is based on the rate of temperature change, as calculated above. If the rate of temperature change is greater than a predetermined threshold value (e.g., 3° C./s), then the heating power of the heating element 144 is lowered to a reduced value (which may be 0%, or 0 Watts, i.e. the heating element 144 is deenergized). The fan speed is set to 100% of its operating range (maximum fan speed) if not already operating at 100%.

A second criterion is based on the temperature difference between the first temperature measurement and the second temperature measurement, ΔT. If the temperature difference is greater than a predetermined threshold value (e.g., 6° C.), then the heating power is lowered to a predetermined percentage (e.g., 25%) of the maximum limit (e.g., 425 W) of the operating range of the heating element 144. The fan speed is set to 100% of its operating range (if not already operating at 100%).

The first criterion and the second criterion may be evaluated simultaneously or nearly simultaneously. For example, the first criterion and the second criterion may be combined in the code executed by the controller 192.

A third criterion is based on the first temperature measurement (taken by the first temperature sensor 180), T_(Room), and the second temperature measurement (taken by the second temperature sensor 184), T_(2NTC). If the first temperature measurement is greater than a predetermined first threshold value (e.g., 32° C.) OR the second temperature measurement is greater than second threshold value (e.g., 35° C.), then the heating power of the heating element 144 is lowered to a reduced value (which may be 0%, or 0 Watts). The fan speed is set to 100% of its operating range (if not already operating at 100%).

A fourth criterion is based on the second temperature measurement (taken by the second temperature sensor 184), T_(2NTC). If the second temperature measurement remains at a temperature greater than a predetermined threshold value (e.g., 35° C.) for longer than a predetermined maximum period of time (e.g., 60 s), then the heating power of the heating element 144 is lowered to (or remains at) 0% of the maximum limit. The fan speed is set to 50% of its operating range (if not already operating at 50%).

A fifth criterion is based on the second temperature measurement (taken by the second temperature sensor 184), T_(2NTC). If the second temperature measurement remains at a temperature greater than a predetermined threshold value (e.g., 35° C.) for longer than a predetermined maximum period of time (e.g., 600 s), then the heater 100 automatically powers down immediately. This criterion ensures that the heater 100 does not endure a prolonged state of abnormal operations.

A sixth criterion is based on the second temperature measurement (taken by the second temperature sensor 184), T_(2NTC). If the second temperature measurement ever rises higher than a predetermined threshold value (e.g., 35° C.) for any reason, then the heater 100 automatically powers down immediately. In this example, the sixth criterion may be the final criterion evaluated, and may be evaluated simultaneously or nearly simultaneously with the fifth criterion. For example, the fifth criterion and the sixth criterion may be combined in the code executed by the controller 192.

As evident from the description above, depending on the type of criteria, some criteria may be evaluated simultaneously and other criteria may be evaluated sequentially, as needed for effective control of the heater. An example of pseudo-code representing the code that may be executed by the controller 192 to analyze the first and second temperature measurements, and based on the six criteria described above, is as follows.

 ReadTemperature_RoomNTC;  ReadTemperature_2NTC;  if ((secondTemp > 45) OR (timeOverTemp > 600000 AND  secondTemp > 35)) {“Shutdown the product.”}  else if (timeOverTemp > 60000 && secondTemp > 35) {“Set motor to  50% and heat element to 0%.”}  else if (secondTemp > 35 OR roomTemp >= 32) {“Set motor to 100%  and heat element to 0%.”}  else if (tempDifference > 6 OR rateTemp > 3) {“Set motor to 100% and  heat element to 25%.”} else {“Temperature control as normal.”}

FIG. 2 is a schematic view of a controller 200 for a heater according to an implementation of the present disclosure. All or part of the controller 200 may correspond to the controller 192 of the heater 100 described above in conjunction with FIG. 1 . The controller 200 may schematically represent one or more modules, control units, components, or the like configured for controlling, monitoring, analyzing and/or timing the operations of various devices or components of the heater 100, as well as controlling or executing one or more steps of any of the methods disclosed herein (such as, for example, steps related to the processing of measurement signals received from the first temperature sensor 180 and the second temperature sensor 184, and the analysis and/or determinations made based on the measurement signals). In addition to the fan 140, heating element 144, first temperature sensor 180, second temperature sensor 184, and user interface 188 shown in FIG. 1 , such devices may include, electrical power (voltage) sources, timing controllers, clocks, frequency/waveform generators, processors, logic circuits, memories, databases, etc. One or more modules of the controller 200 may be, or be embodied in, one or more devices located outside or separate from the heater 100, for example, a computer workstation, desktop computer, laptop computer, portable computer, tablet computer, handheld computer, mobile computing device, personal digital assistant (PDA), smartphone, etc. One or more modules of the controller 200 may communicate with one or more other modules via one or more busses or other types of communication lines or wireless links, as appreciated by persons skilled in the art.

In the illustrated implementation, the controller 200 includes one or more electronics-based processors 202, which may be representative of a main electronic processor providing overall control, and one or more electronic processors configured for dedicated control operations or specific signal processing tasks (e.g., a graphics processing unit or GPU, a digital signal processor or DSP, an application-specific integrated circuit or ASIC, a field-programmable gate array or FPGA, etc.). The controller 200 also includes one or more memories 204 (volatile and/or non-volatile types, e.g. RAM and/or ROM) for storing data and/or software. Stored data may be organized, for example, in one or more databases or look-up tables. The controller 200 may also include one or more device drivers 206 for controlling one or more types of user interface devices (e.g., the user interface device 188 described above in conjunction with claim 1) and providing an interface between the user interface devices and components of the controller 200 communicating with the user interface devices. Such user interface devices may include user input devices 208 (e.g., keyboard, keypad, touch screen, mouse, joystick, trackball, and the like) and user output devices 210 (e.g., display screen, printer, visual indicators or alerts, audible indicators or alerts, and the like). In various implementations, the controller 200 may be considered as including one or more of the user input devices 208 and/or user output devices 210, or at least as communicating with them. In the example of FIG. 1 and as noted above, the user interface device 188 may include both user input devices 208 and user output devices 210.

In some implementations, the controller 200 may also include one or more types of computer programs or software contained in memory and/or on one or more types of non-transitory (or tangible) computer-readable media. One or more devices of the controller 200 may be configured to receive and read (and optionally write to) the computer-readable media. The computer programs or software may contain non-transitory instructions (e.g., logic instructions) for controlling or performing various operations of the heater 100, such as, for example, analysis of temperature measurement and control. The computer programs or software may include system software and application software. System software may include an operating system (e.g., a Microsoft Windows® operating system) for controlling and managing various functions of the controller 200, including interaction between hardware and application software. In particular, the operating system may provide a graphical user interface (GUI) displayable via a user output device 210, and with which a user may interact with the use of a user input device 208. Application software may include software configured to control or execute various operations of the heater 100, and/or some or all of the steps of any of the methods disclosed herein.

The controller 200 may also include a fan controller (or control module) 212 configured to control the operation of the fan 140, particularly the fan motor 164 (FIG. 1 ), and a heating element controller (or control module) 214 configured to control the operation of the heating element(s) 144 (FIG. 1 ). The controller 200 may also include one or more sensor interfaces 216 configured to receive and process feedback (e.g., measurement) signals received from the first temperature sensor 180 and the second temperature sensor 184 (FIG. 1 ). For example, the sensor interfaces 216 may be embodied in different pieces of firmware or other electronic circuitry that are part of a microcontroller of the controller 200. The sensor interfaces 216 may communicate with the fan controller 212 and the heating element controller 214 as needed to provide effective control of various operating parameters such as heating power and fan speed as described herein. The firmware or other electronic circuitry embodying the fan controller 212 and the heating element controller 214 also may be provided with the same microcontroller that includes the sensor interfaces 216, or may be provided with separate hardware of the controller 200. The controller 200 may also include an analyzing module 218 configured to receive the temperature measurement signals (which may first be received and processed by the sensor interfaces 216) produced by the first temperature sensor 180 and the second temperature sensor 184, process the temperature measurement signals, and accordingly carry out one or more steps of one or more of the methods described herein such as making determinations as to heating power and fan speed, and transmitting control signals to the heating element controller 214 and/or the fan controller 212 to make adjustments to heating power and/or fan speed. The operations of the fan controller 212, the heating element controller 214, the sensor interfaces 216, and the analyzing module 218 may be coordinated or synchronized with each other as needed to provide effective control of the heater 100 according to implementations described herein.

FIG. 3 is a flow diagram 300 illustrating an example of a method for operating a heater (such as the heater 100 described above in conjunction with FIG. 1 ) according to an implementation of the present disclosure. In the method, the heater 100 is operated at a preset (or pre-existing, or current) heating power of the heating element 144 and a preset (or pre-existing, or current) fan speed of the fan 140, to intake ambient air 168 through the inlet 128 and into the air duct 136, heat internal air 172 in the air duct 136, and discharge the heated air 176 from the air duct 136 and through the outlet 132 (step 302). A first measurement of a first temperature of the ambient air 168 at the inlet 128 and a second measurement of a second temperature of internal, heated air 172 in the air duct 136 are then made (step 304). In other words, readings from the first temperature sensor 180 and the second temperature sensor 184 are taken, which may be done simultaneously or nearly simultaneously. A determination is then made as to whether one or more criteria (such as described above) have bene met (step 306). The criteria are based on (or derived from) the second measurement, or both the first measurement and the second measurement. If none of the one or more criteria has been met, the heater 100 is allowed to continue to operate at the preset heating power and the preset fan speed (step 308). On the other hand, if any of the one or more criteria has been met, the preset heating power, or the preset fan speed, or both the preset heating power and the preset fan speed, is adjusted (step 310).

In an implementation, one or more steps of the method just described may be controlled or performed by a controller such as the controller 192 or 200 described above in conjunction with FIG. 1 or 2 .

In an implementation, the flow diagram 300 may represent a heater (e.g., heater 100 shown in FIG. 1 ) configured to carry out the steps 302-310. For this purpose, a controller (e.g., the controller 192 or 200 shown in FIG. 1 or 2 ) including a processor, memory, and other components as appreciated by persons skilled in the art, may be provided to control the performance of one or more of the steps 302-310, such as by controlling the components of the heater 100 involved in carrying out one or more of the steps 302-310.

It will be understood that one or more of the processes, sub-processes, and process steps described herein may be performed by hardware, firmware, software, or a combination of two or more of the foregoing, on one or more electronic or digitally-controlled devices. The software may reside in a software memory (not shown) in a suitable electronic processing component or system such as, for example, the system controller 192 or 200 schematically depicted in FIG. 4 or 5 . The software memory may include an ordered listing of executable instructions for implementing logical functions (that is, “logic” that may be implemented in digital form such as digital circuitry or source code, or in analog form such as an analog source such as an analog electrical, sound, or video signal). The instructions may be executed within a processing module, which includes, for example, one or more microprocessors, general purpose processors, combinations of processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate array (FPGAs), etc. Further, the schematic diagrams describe a logical division of functions having physical (hardware and/or software) implementations that are not limited by architecture or the physical layout of the functions. The examples of systems described herein may be implemented in a variety of configurations and operate as hardware/software components in a single hardware/software unit, or in separate hardware/software units.

The executable instructions may be implemented as a computer program product having instructions stored therein which, when executed by a processing module of an electronic system (e.g., the system controller 192 or 200 schematically depicted in FIG. 4 or 5 ), direct the electronic system to carry out the instructions. The computer program product may be selectively embodied in any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as an electronic computer-based system, processor-containing system, or other system that may selectively fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this disclosure, a computer-readable storage medium is any non-transitory means that may store the program for use by or in connection with the instruction execution system, apparatus, or device. The non-transitory computer-readable storage medium may selectively be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device. A non-exhaustive list of more specific examples of non-transitory computer readable media include: an electrical connection having one or more wires (electronic); a portable computer diskette (magnetic); a random access memory (electronic); a read-only memory (electronic); an erasable programmable read only memory such as, for example, flash memory (electronic); a compact disc memory such as, for example, CD-ROM, CD-R, CD-RW (optical); and digital versatile disc memory, i.e., DVD (optical). Note that the non-transitory computer-readable storage medium may even be paper or another suitable medium upon which the program is printed, as the program may be electronically captured via, for instance, optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner if necessary, and then stored in a computer memory or machine memory.

It will also be understood that the term “in signal communication” or “in electrical communication” as used herein means that two or more systems, devices, components, modules, or sub-modules are capable of communicating with each other via signals that travel over some type of signal path. The signals may be communication, power, data, or energy signals, which may communicate information, power, or energy from a first system, device, component, module, or sub-module to a second system, device, component, module, or sub-module along a signal path between the first and second system, device, component, module, or sub-module. The signal paths may include physical, electrical, magnetic, electromagnetic, electrochemical, optical, wired, or wireless connections. The signal paths may also include additional systems, devices, components, modules, or sub-modules between the first and second system, device, component, module, or sub-module.

More generally, terms such as “communicate” and “in . . . communication with” (for example, a first component “communicates with” or “is in communication with” a second component) are used herein to indicate a structural, functional, mechanical, electrical, signal, optical, magnetic, electromagnetic, ionic or fluidic relationship between two or more components or elements. As such, the fact that one component is said to communicate with a second component is not intended to exclude the possibility that additional components may be present between, and/or operatively associated or engaged with, the first and second components.

It will be understood that various aspects or details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims. 

What is claimed is:
 1. A heater for heating air, the heater comprising: a housing comprising an inlet, an outlet, and an air duct between the inlet and the outlet; a fan positioned in the air duct and configured to establish a flow of air from an ambient space outside the housing into the inlet, through the air duct, and to the outlet; a heating element positioned in the air duct and configured to heat the air flowing through the air duct; a first temperature sensor positioned at or near the inlet and configured to measure a first temperature of ambient air at the inlet; and a second temperature sensor positioned in the air duct and configured to measure a second temperature of heated air flowing through the air duct.
 2. The heater of claim 1, wherein the second temperature sensor is positioned at one of the following positions: at the heating element and spaced from the heating element; between the heating element and the outlet; between the heating element and the outlet, and closer to the heating element than to the outlet.
 3. The heater of claim 1, wherein the first temperature sensor and the second temperature sensor each are configured as one of: a thermistor; a negative temperature coefficient (NTC) sensor; a resistance temperature detector (RTD); a thermocouple.
 4. The heater of claim 1, wherein the air duct comprises a top side and an opposing bottom side, the first temperature sensor is positioned at the top side, and the second temperature sensor is positioned at the bottom side.
 5. The heater of claim 1, comprising a controller configured to control a preset heating power of the heating element and a preset fan speed of the fan.
 6. The heater of claim 5, wherein the controller is configured to control the preset heating power and the preset fan speed based on measurement signals received by the controller from the second temperature sensor, or from both the first temperature sensor and the second temperature sensor.
 7. The heater of claim 5, wherein the controller is configured to control an operation comprising the following: receiving from the first temperature sensor a first measurement of a first temperature of the ambient air at the inlet; receiving from the second temperature sensor a second measurement of a second temperature of heated air in the air duct; and determining if one or more criteria have been met, wherein the one or more criteria are based on the second measurement, or both the first measurement and the second measurement, and wherein: if none of the one or more criteria has been met, continuing to operate the heater at the preset heating power and the preset fan speed; and if any of the one or more criteria has been met, adjusting the preset heating power, or adjusting the preset fan speed, or adjusting both the preset heating power and the preset fan speed.
 8. The heater of claim 7, wherein the one or more criteria are based on a running average of the second measurement, or running averages of both the first measurement and the second measurement.
 9. The heater of claim 7, comprising calculating a rate of temperature change, wherein the one or more criteria comprise: if the rate of temperature change is greater than a predetermined threshold value, then lowering the heating power of the heating element to a reduced value.
 10. The heater of claim 9, wherein the reduced value is 0% of a maximum limit of the heating power at which the heating element operates.
 11. The heater of claim 9, wherein the one or more criteria further comprise: if the rate of temperature change is greater than the predetermined threshold value, then increasing the preset fan speed.
 12. The heater of claim 11, wherein the preset fan speed is increased to 100% of a maximum limit at which the fan operates.
 13. The heater of claim 7, comprising calculating a temperature difference between the first measurement and the second measurement, wherein the one or more criteria comprise: if the temperature difference is greater than a predetermined threshold value, then lowering the heating power to a reduced value.
 14. The heater of claim 13, wherein the one or more criteria further comprise: if the rate of temperature change is greater than a predetermined threshold value, then increasing the preset fan speed.
 15. The heater of claim 14, wherein the preset fan speed is increased to 100% of a maximum limit at which the fan operates.
 16. The heater of claim 7, wherein the one or more criteria comprise: if the first temperature measurement is greater than a predetermined first threshold value or the second temperature measurement is greater than a predetermined second threshold value, then lowering the heating power to a reduced value.
 17. The heater of claim 16, wherein the reduced value is 0% of a maximum limit of the heating power at which the heating element operates.
 18. The heater of claim 16, wherein the one or more criteria further comprise: if the first temperature measurement is greater than the predetermined first threshold value or the second temperature measurement is greater than the predetermined second threshold value, then if the rate of temperature change is greater than the predetermined threshold value, then increasing the preset fan speed.
 19. The heater of claim 18, wherein the preset fan speed is increased to 100% of a maximum limit at which the fan operates.
 20. The heater of claim 7, wherein the one or more criteria comprise: if the second temperature measurement remains at a temperature greater than a predetermined first threshold value for longer than a predetermined first period of time, then lowering the heating power to, or maintaining the heating power at, 0% of a maximum limit of the heating power at which the heating element operates.
 21. The heater of claim 20, wherein the one or more criteria comprise: if the second temperature measurement remains at a temperature greater than the predetermined second threshold value for longer than a predetermined second period of time that is longer than the predetermined first period of time, then powering down the heater.
 22. The heater of claim 7, wherein the one or more criteria comprise: if the second temperature measurement is greater than a predetermined threshold value, then powering down the heater.
 23. A method for operating a heater comprising an inlet, an outlet, an air duct between the inlet and the outlet, a fan, and a heating element, the method comprising: operating the heater at a preset heating power of the heating element and a preset fan speed of the fan, to intake ambient air through the inlet and into the air duct, heat air in the air duct, and discharge the heated air through the outlet; making a first measurement of a first temperature of the ambient air at the inlet; making a second measurement of a second temperature of heated air in the air duct; and determining if one or more criteria have been met, wherein the one or more criteria are based on the second measurement, or both the first measurement and the second measurement, and wherein: if none of the one or more criteria has been met, continuing to operate the heater at the preset heating power and the preset fan speed; and if any of the one or more criteria has been met, adjusting the preset heating power, or adjusting the preset fan speed, or adjusting both the preset heating power and the preset fan speed. 